As a proposal of this type, there is Japanese Unexamined Utility Model Publication (Kokai) No. Heisei 4-95567, entitled "Traveling System for Mobile Telescopic Aerial Platform". In the prior art disclosed in the above-identified publication, two driving wheels are provided at positions on one diagonal line of a vehicle body, and two idler wheels are provided at the positions on the other diagonal line. By turning of the driving wheels, the mobile telescopic aerial platform is turned toward a desired direction and travels. In the prior art shown in the publication, a selection switch and a foot switch are provided for permitting an operator to select a desired traveling mode among traveling modes of longitudinal straight traveling, oblique traveling, transverse traveling, transverse turning and so forth. After selection of the desired traveling mode by the selection switch, when the foot switch is depressed by the operator, the driving wheels are once turned into a predetermined initial position and subsequently turned into positions adapted to the selected traveling mode. For instance, when the foot switch is depressed after switching the switch into longitudinal straight traveling position, two driving wheels 1a and 1b are turned into the straight traveling position oriented to straight traveling direction (arrow a), as shown in FIG. 1. Also, as shown in FIG. 2, when the foot switch is depressed after switching of the selection switch into oblique traveling position, two driving wheels 1a and 1b are initially turned into the straight traveling position oriented to the straight traveling direction (arrow a) similarly to FIG. 1. Subsequently, the driving wheels 1a and 1b are turned into the position adapted to oblique traveling. On the other hand, when the foot switch is depressed after switching the select switch into the transverse slalom traveling, two driving wheels 1a and 1b are turned into transverse traveling position oriented in transverse direction (arrow b).
Also, as a proposal for moving the traveling vehicle in various desired direction, there is Japanese Unexamined patent Publication No. Heisei 3-235762, entitled "Steering System for Traveling Vehicle". In the prior art disclosed in this publication, two steering and driving wheels and two idler wheels are provided on the vehicle body. The steering and driving wheels are operated to perform longitudinal straight traveling, longitudinal direction turning, transverse traveling, oblique traveling, spin turning and so forth for moving the vehicle a desired direction associated with work to be done. The steering and driving wheels are connected to a cylinder via a link so that the steering and driving wheels are steered by expansion and contraction of the cylinder. In addition, a limit switch which turns ON and OFF depending upon the expansion and contraction stroke of the cylinder is provided. Also, on an operation panel, a traveling direction changeover switch and steering switch are provided so that expansion and contraction of the cylinder is controlled by ON and OFF operation of the traveling direction changeover switch and the steering switch as well as ON and OFF action of the limit switch to change orientation of the steering and driving wheels to travel in the desired direction.
In such prior art, in case of the former prior art disclosed in Japanese Unexamined Utility Model Publication No. Heisei 4-95567, when the operator performs traveling operation, the operator selects the traveling mode, i.e. longitudinal straight traveling, longitudinal direction turning, transverse traveling, oblique traveling, spin turning and so forth, then depresses the foot switch and initiates traveling in the direction toward which the driving wheels are turned after confirming completion of turning of the driving wheels. Accordingly, when the traveling modes are frequently switched during traveling associated with the work to be done, the operation becomes troublesome. Also, the vehicle cannot travel in a period from immediately after switching of the traveling mode to completion of turning of the driving wheels, to make it impossible to quickly move in the desired direction.
On the other hand, in the latter case disclosed in Japanese Unexamined Patent Publication No. Heisei 3-235762, the operator is required to simultaneously operate the traveling direction changeover switch and the steering switch to make operation cumbersome. Furthermore, since the orientation of the steering and driving wheels is detected by the limit switch, the construction becomes complicated and adjustment of the limit switch is time consuming.
The present invention is designed to solve the defects in the prior art and thus, the first object is to provide an operation control system for a traveling vehicle which is less troublesome in operation upon frequently switching traveling modes to shorten a period from immediately after switching of the traveling mode to completion of turning of the driving wheels so that the operation for moving in the desired direction can be easily and quickly done.
The second object of the present invention is to provide an operation control system for a traveling vehicle which simplifies operation, determines steering angle of steering and driving wheels by a command value from a controller to make the normally required limit switch unnecessary for simplification of construction and avoidance of adjustment of position.